Magnetic cores used for a motor or the like are conventionally made by compacting powder for a powder magnetic core. The powder for making a powder magnetic core is composed of magnetic particles. Each of the magnetic particles has a surface coated with an insulating layer for securing electric insulation between the compacted magnetic particles.
Examples of the powder for a powder magnetic core include a powder for a powder magnetic core comprising magnetic particles and having a surface coated with a high insulating polymer resin such as a silicone resin that forms an insulating resin layer as the insulating layer, and a powder for a powder magnetic core comprising magnet particles and having a surface deposited with an oxide such as silica (SiO2) by chemical vapor deposition (CVD) that forms an oxide insulating layer as the insulating layer. Furthermore, a powder for a powder magnetic core comprising magnetic particles and having an insulating layer formed of an oxide insulating layer and a silicone resin insulating layer (i.e. polymer resin insulating layer) in series from the magnetic particle surface in a thickness direction has been proposed. (For example, refer to Patent Documents 1 and 2.)    Patent Document 1: JP Patent Publication (Kokai) No. 2006-233295A    Patent Document 2: JP Patent Publication (Kokai) No. 2008-88505A